The invention relates generally to the field of printing and, more particularly, to a method of making a printing apparatus that utilizes pumps having piezoelectric transducers with functionally gradient activation elements.
Piezoelectric pumping mechanisms are widely used for ink flow and drop ejection in a variety of ink jet printing apparatus. Conventional piezoelectric pumps utilize piezoelectric transducers that comprise one or more uniformly polarized piezoelectric elements with attached surface electrodes. The three most common transducer configurations are multilayer ceramic, monomorph or bimorphs, and flextensional composite transducers. To activate a transducer, a voltage is applied across its electrodes thereby creating an electric field throughout the piezoelectric elements. This field induces a change in the geometry of the piezoelectric elements resulting in elongation, contraction, shear or combinations thereof. The induced geometric distortion of the elements can be used to implement motion or perform work. In particular, piezoelectric bimorph transducers, which produces a bending motion, are commonly used in micropumping devices. However, a drawback of the conventional piezoelectric bimorph transducers is that two bonded piezoelectric elements are needed to implement the bending. These bimorph transducers are difficult and costly to manufacture for micropumping applications (in this application, the word micro means that the dimensions of the apparatus range from 100 microns to 10 mm). Also, when multiple bonded elements are used, stress induced in the elements due to their constrained motion can damage or fracture an element due to abrupt changes in material properties and strain at material interfaces.
Therefore, a need persists for a method of making a printing apparatus that provides for a plurality of independent piezoelectric pumps each utilizing a functionally gradient piezoelectric transducer that overcomes the aforementioned problems associated with conventional pumping apparatus.
It is, therefore, an object of the present invention to provide a method of making a printing apparatus which includes a plurality of piezoelectric pumps each of which utilizes a transducer in which the pumping action is accomplished with a single functionally gradient piezoelectric element.
To accomplish these and other objects an advantages of the invention, there is provided a method of making a printing apparatus configured for drawing fluid from a fluid reservoir and then ejecting droplets of fluid onto a receiver to form an image, comprising the steps of:
(a) providing an orifice manifold having a plurality of spaced orifices through which droplets of fluid are ejected;
(b) providing a plurality of adjoining independent piezoelectric pumps, each having an inlet port and an outlet port, said piezoelectric pumps comprising a pump body having an interior fluid compartment, and means for controlling fluid passing through said inlet and outlet ports;
(c) arranging each one of said plurality of piezoelectric pumps so that an outlet port is in fluid communications with one of said spaced orifices of said manifold;
(d) arranging a piezoelectric transducer in said pump of each one of said plurality of piezoelectric pumps, each one of said piezoelectric transducers comprising a functionally gradient piezoelectric element having opposed first and second surfaces and a first electrode fixedly arranged on said first surface and a second electrode fixedly arranged on said second surface, said piezoelectric element being formed of piezoelectric material having a functionally gradient dcoefficient selected so that the functionally gradient piezoelectric element changes geometry in response to an applied voltage to said first and second electrodes which produces an electric field in the functionally gradient piezoelectric element;
(e) providing a plurality of power sources, each having first and second terminals connected respectively to said first and second electrodes of each one of said piezoelectric transducers for enabling fluid flow through a respective fluid reservoir;
(f) operably connecting each one of said plurality of power sources to one of said plurality of piezoelectric pumps;
(g) energizing any one of said piezoelectric transducers to pump fluid from said fluid reservoir then through said inlet port of said interior fluid compartment in at least one of said pumps and then through said orifice in fluid communications therewith of said orifice manifold thereby forming an ejected droplet of fluid; and
(h) positioning the receiver in proximity to said orifice manifold for receiving said ejected droplet of fluid so as to form an image thereon.
Accordingly, an advantageous effect of the method of the invention is that it utilizes pumps that implement fluid motion with the use of a single functionally gradient piezoelectric thereby eliminating the need for multilayered or composite piezoelectric structures. This eliminates the need for multiple electrodes and associated drive electronics; and it minimizes or eliminates stress induced fracturing that occurs in multilayered or composite piezoelectric structures.